The invention relates to a process for manufacturing moulded coke and a vertical furnace for manufacturing said coke in which the heating and coking heat is provided by an electric supply of energy and transferred by a recycled current of gas. The invention also relates to an electrical heating process and device untilizing a fluid-conducting granulated bed.
Processes are known for manufacturing moulded coke in a vertical furnace in which a heap of moulded coal ovoids circulates downwardly in a counter-current manner relative to a recycled current of gas coming from a fraction of the gas produced by the coking and taken from the top of the furnace and re-introduced at the base of the latter.
The moulded ovods are coked in a median zone of the furnace by a gaseous supply from the distillation.
It has been proposed to achieve this supply of heat, initially produced by means of burners, by the dissipation of electrical energy by the Joule effect, which has for result to avoid the dilution of the coking gases recovered at the top of the furnace by the smoke resulting from the combustion, whose volume is large, in particular when the burners are supplied with air, and thus considerably increase the calorific value of the coking gases recovered at the top of the furnace.
In a first manner of tackling the problem, the calorific energy was supplied by an outer electrical heating, of the electrical resistance furnace type, however, this technique has a poor yield and efficiency, since the heap of coke is not uniformly heated. Indeed, the coke undergoes at the walls an excessive overheating which is excessively rapid and has an adverse effect on the mechanical behaviour of the ovoids (bursting and cracking) and on their metallurgical quality (re-activity).
Various publications, namely the patents FR-A-628,168, US-A-2,127,542, DE-A-409,341 and FR-A-2,529,220, have proposed for solving these problems, to supply the calorific coking energy directly in the concerned zone by supplying electrical energy to the heap of hot ovoids by generating electrical currents between diametrically opposed electrodes separated by the heap of ovoids to be coked.
In patent FR-A-2,529,220, the vertical furnace is in the form of a column having a cross-sectional shape which is substantially uniform throughout the inner height of the bed of moulded ovoids in circulation, and comprises, on one hand, electrodes disposed in a median zone of the lateral wall of the furnace, and, on the other hand, movable electrodes which are introduced through the upper part of the furnace into the bed of circulating ovoids and disposed in an adjustable manner at a level of the furnace higher than that of the fixed electrodes.
One of the major drawbacks of this type of furnace resides in the difficulty of ensuring an apropriate electrical conductivity of the bed of circulating moulded coal ovoids so as to regulate in a homogeneous and optimum manner the supply of heat required for the coking of the ovoids Indeed, the electrical conductivity of the mass of ovoids is related, partly, to the quality and the reproducibility of the individual contacts of the ovoids with one another, and therefore to the distribution of the internal pressures of this mass obtained by compacting. Now, an excessive local or general compacting of this bed constitutes a hindrance to the "fluid" flow of the materials and to a correct circulation of the bed, which is not acceptable.
Further, the passage of a localized current producing a localized heating by the Joule effect of the mass of ovoids considerably reduces the resistivity and results in a concentration of the electrical currents in a zone which is already excessively hot.
This difficulty is not suitably mastered by the means described hereinbefore and the regulation of the thermal equilibrium of the circulating ovoid bed is not ensured, which is however necessary for the control of the quality of the baking of the ovoids (namely progressive, regular, homogeneous and precise).